Abstract

Part I . The binding of [beta]-cyclodextrin ([beta]-CD) with sugars was studied using "inhibition kinetics". The rates of hydrolysis of trimethyl orthobenzoate and benzaldehyde dimethyl acetal in acidic solution were monitored using a single beam stopped-flow spectrophotometer. Both substrates exhibit saturation kinetics and 1:1 binding with [beta]-CD, and the rates of hydrolysis are retarded by the cyclodextrin, in agreement with earlier studies. The retarded rates of hydrolysis in the presence of [beta]-CD are modulated by the addition of guests that bind to the CD, and "inhibition constants" (K 1 ) may be determined. Several aldoses were studied. Pentoses were found to bind modestly to [beta]-CD (K 1 = 100-1000 mM) and hexoses hardly bind at all (K 1 > 500 mM). The results obtained with the two probe reactions agree well with each other, and the K 1 values are compared to the disparate values in literature. Part II . The aqueous bromination of 2-aminopyrimidine (2-AP) involves two major steps, and the first step forms an addition product, an intermediate that was previously observed by NMR. The second step, which is quite slow, involves elimination of water from the intermediate to Yield the 5-bromo derivative. The focus of this investigation was on the initial fast step to try to discover how the intermediate is formed. The kinetics of the bromination of 2-aminopyrimidine and several related derivatives have been studied using a stopped-flow apparatus. The mechanisms were investigated by constructing pH-rate profiles for each compound. The pH-rate profiles for 2-aminopyrimidine and 1,2-dihydro-2-imino-1-methyl-pyrimidine (M2A) demonstrate the complexity of these reactions and the evidence that more than one mechanism is involved. This statement is especially true for the latter compound where mixed orders of reactions were found. For comparative purposes the kinetics of bromination of 2-amino-4,6-dimethyl-pydmidine (2-ADP), 2-aminopyridine (2-APy), 2-dimethylaminopyridine (2-DAPy), aniline and N,N -dimethylaniline were also studied.